<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <script>
    //字符串
    let str = 'i want you';

    //截取
    str.slice(2, 6).toUpperCase().toLowerCase().split('');

    //数组
    let arr = [1,2,3,4,5,6];

    console.log(arr.map(item => item * 100).filter(item => item > 100).slice(1, 4))


  </script>
</body>
</html>